Currently, in widely-adopted OLED devices, the light-emitting layer thereof is formed by mixing host and dopant. Each dopant needs to go with its appropriate host material and the ratio therebetween tremendously influences the efficiency of OLED devices. However, it is extremely difficult to control the concentration and uniformity of the dopant. In order to resolve this problem, sophisticated and complicated equipment is required which correspondingly increases the cost of production. Therefore, development of an OLED device with a simple manufacturing process, and improved efficiency is desirable.
In a conventional light-emitting layer formed by mixing host and dopant, the ratio between host and dopant and the uniformity of dopant need to be considered. Since the whole host can emit light, the light-emitting area may be transferred with the alteration of operating voltage. When manufacturing a white OLED device, a light-emitting layer comprising various mixtures of host and dopant or one host doped with two or more dopants is required. However, the light color of the white OLED device is altered with the operating voltage or brightness. Therefore, when manufacturing a white OLED device, only the precise control of parameters and the use of sophisticated equipment can improve the yield.